The present invention relates generally to vehicles and, more particularly, to methods of producing carpeting utilized within vehicles.
It is generally considered desirable to reduce the level of noise within a vehicle passenger compartment. External noises, such as road noise, engine noise, vibrations, etc., as well as noises emanating from within passenger compartments, may be attenuated through the use of various acoustical materials. Accordingly, sound attenuating materials for vehicles, such as automobiles, are conventionally used in dashboards, in conjunction with carpeting for floor panels, in wheel wells, in trunk compartments, under hoods, as part of headliners, etc.
The attenuation of external noise (i.e., noise emanating from a source external to a vehicle compartment) is conventionally referred to as sound transmission loss (STL). The attenuation of internal noise (i.e., noise emanating from within a vehicle compartment) is conventionally referred to as sound absorption. The acoustic impedance of a material is defined as material density times acoustic velocity, and is expressed in units of Rayls (Newton-seconds/meter3). Acoustic impedance defines how easy it is for air to move through a material. Thus, for fibrous materials, acoustic impedance may depend upon the density of the fibrous material and fiber diameter. Generally, the heavier the blanket and the finer the fibers, the higher the acoustic impedance. Moreover, thicker layers typically have more acoustic impedance than thin layers. The ability of a material to attenuate noise is conventionally defined by the material""s collective STL, acoustic impedance, and absorption characteristics.
Carpeting for use within vehicles is conventionally tufted or nonwoven. Tufted carpet generally includes a composite structure in which tufts, or bundles of carpet fibers are introduced (such as by stitching) into a primary backing, such as a woven or non-woven fabric. A secondary backing or coating of thermoplastic material is then applied to the underside of the carpet construction in order to securely retain the tufted material in the primary backing. This secondary backing not only dimensionally stabilizes the construction but can also provide greater abrasion and wear resistance, and may serve as an adhesive for an additional layer of material. Nonwoven carpet is composed of fiber that is mechanically entangled by needling, water jet, or other process.
Vehicle carpeting is conventionally molded into a non-planar three dimensional contoured configuration which conforms to the contours of a vehicle floor. A secondary coating of thermoplastic material applied to the primary backing may also make the carpeting moldable and shape-sustaining, and may also serve as a barrier to improve the sound attenuating properties of the carpeting.
Conventional vehicle carpeting typically includes an ethylene-vinylacetate (EVA), polyethylene (PE), or polyvinylchloride (PVC) layer which serves as a barrier sheet. Unfortunately, there are several drawbacks associated with the use of EVA, PE, and PVC layers in these vehicle applications. For example, EVA, PE, and PVC are non-porous materials which can be relatively heavy when applied to carpeting, dash insulators, and other interior trim components.
In general, the ability of conventional vehicle carpeting to attenuate sound increases as the amount of material increases. Unfortunately, increased carpeting material often increases the weight as well as the cost of vehicle carpeting, which is typically undesirable. Accordingly, there is a continuing need for carpet materials for use within vehicles that exhibit good sound attenuating properties and that are also lightweight and low in cost.
In view of the above discussion, porous carpet for use within vehicles and methods of producing same are provided. According to embodiments of the present invention a primary layer of thermoplastic fibrous material (woven or non-woven) is provided. The primary layer has opposite first and second sides, with fiber (e.g., yarn, etc.) tufts extending outwardly from the first side. The primary layer may be heated (although not required) to a predetermined temperature (e.g., about 150xc2x0 F. to about 250xc2x0 F.). A secondary layer of thermoplastic material (e.g., polyethylene, ethylene vinyl acetate, etc.) having a temperature of between about 350xc2x0 F. and about 500xc2x0 F. is applied to the primary layer such that the secondary layer penetrates the primary layer up to about 90% of a thickness of the primary layer and forms a carpet backing. The carpet backing is then heated to a temperature sufficient to cause the carpet backing to achieve a fluid state. The heated carpet backing is then subjected to sufficient vacuum such that air is drawn through the heated carpet backing to create a porous carpet structure.
According to embodiments of the present invention, a layer of porous thermoformable material may be applied to the porous carpet backing to hold the porous carpet backing open such that air can flow therethrough and to provide additional mechanical strength. The layer of porous thermoformable material may be fibrous material selected from the group consisting of natural fibers, man-made fibers, and blends of natural fibers and man-made fibers.
Porous carpet according to embodiments of the present invention can provide desired sound deadening and absorption properties within vehicles. Moreover, porous carpet according to embodiments of the present invention may have reduced overall weight without sacrificing sound attenuating properties.